acid in a graduated cylinder, the increase in volume of the lower layer
giving the percentage by volume of the bases. These may also be deter-
mined directly by collecting the acid liquid, carefully adding to it a large
excess of caustic soda solution (D 1-40), and measuring the bases which
The specific gravity of the light oils usually lies between 0-900 and 0-950.
Normal oils give about 90% of distillate up to 200° and have the specific gravity
0-930 ; they contain 5-15% of phenols and 1-3% of bases.
MIDDLE AND HEAVY TAR OILS
With these the following determinations are made :
1. Determination of the Specific Gravity.—As with light oils.
2. Distillation.—This is carried out either with the product as it
stands, which is distilled from a flask with a long side-tube but no condenser
(to prevent crystallisation of naphthalene), or with the product free from
naphthalene, or with that free also from phenols and bases, resulting from
determinations 3 and 4.
3. Determination of the Crude Naphthalene.—From 0-5 to 2 kilos
of the oil is left for 24 hours at 15° and then cooled if necessary to cause
the naphthalene to crystallise, this being pumped off on a cloth or paper
filter, pressed in a press until all the oily part is removed and weighed.
This represents the crude naphthalene, of which the melting and boiling
points may be determined.
4. Other Determinations.—The oil free from naphthalene is treated
with caustic soda to determine the phenols, and with dilute sulphuric acid
to determine the pyridine bases, as with the light oils (3 and 4).
A good middle oil has a specific gravity not less than i ; at least 90 % of it
distil below 260°, and it contains not less than 30% of crude naphthalene (b.p.
210-220°). The naphthalene-free oil has the specific gravity 0-99-1-01, and
contains 25-35% °f phenols (about one-third of this being carbolic acid) and
about 5% of bases.
The heavy oils have a mean specific gravity 1-04 and distil between 200°
and 300° ; they contain mainly naphthalene and other solid hydrocarbons,
together with 8-10% of phenols (principally cresols and higher homologues)
and about 6% of pyridine bases.
The analysis of anthracene oils includes, besides determinations of the
specific gravity and of the behaviour on distillation—which are carried
out as with the middle oils—only the determination of the anthracene,
which is effected by transforming it into anthraquinone by means of chromic
acid (see later: Anthracene, i).
Anthracene oils have the specific gravity about i-i and boil between 280°
and 400°; they are solid at the ordinary temperature and fluid at 60° and
contain 2-5-3-5% of pure anthracene and about 6% of higher phenols. 20% sulphuric